1. Field of the Invention
The present invention relates to a distance measurement apparatus of a gamma ray source, using a multilayered ray detector.
2. Description of the Related Art
A radiation detection system, which detects rays such as hard X-rays and γ-rays to generate image information, is used in various technical fields. For example, when a radiation field from a certain celestial body is detected, the physical state or structure of the celestial body can be studied. Moreover, when a human body is irradiated with X-rays, and the transmitted waves are analyzed, it is possible to acquire a tomographic image. This system is also used in other fields, such as atomic energy (glass solidification inspection of radiation waste, radiation monitoring apparatuses, and the like), nondestructive testing (semiconductor inspection apparatuses), and a resource search field mineral exploration (underground exploration).
However, in most of the related-art radiation detection systems, radiation energy is measured based on photons impacting on a detector surface, for forming an image. It is not possible to measure the direction the rays are traveling in, or the distance to the ray source, using this type of detection system.
With regard to measuring distance from the ray source, techniques such as that disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-294652, are known. In this technique, two detectors are arranged, for counting the number of incident gamma rays in a predetermined positional relation, and distance to the gamma ray source is estimated based on the ratio of numbers of rays received by each detector. When the gamma ray source exists right under a detector, the distance can be obtained. However, when the gamma ray source does not exist right under the detector, the detection value becomes indefinite because of a dead angle, and the distance to the ray source cannot be obtained with a high precision.